Trail Section 23 - Falls Lake Trail Geologic Guide

 

Geologic Map Trail Section 23

Geologic information by Edward F. Stoddard (in Bold Text).

Mileage and Trail section descriptions from Mark Edelstein with updates from March – April 2011.

 

Section 23 (Red Mill Road to Old Oxford Highway)

15.8 – From this small parking area, step over the chain barrier to start on an open roadbed, heading W.

We will be walking parallel to the Eno River for this section.  Just downhill to the right, the topographic map shows that the river has a small oxbow, formed when the river abandoned an old meander loop by cutting a new shorter path across its neck.

16.0 – Turn slight L off the roadbed onto a narrow footpath.

16.1 – Start to walk along a large farm field, L.

16.3 – Veer R as the footpath moves away from the field and goes through a more open forest.

23-A:  Here the trail crosses, in an oblique fashion, a ridge that runs north-northeast.  The ridge is the result of a large diabase dike.  This is a good place to try to determine the size and orientation of the dike, by surveying the diabase chunks, and remembering that loose chunks can only move downhill from their original positions (unless humans help out).  You can also go up to the edge of the large field and look for diabase pieces that may have been cleared to the field's edge.

16.6 – Pass through a wet area with a water run. Soon pass under a powerline (footing may be wet).

23-B:  There are good outcrops of diabase.

23-C:  Still more large blocks of diabase.  It appears that the trail has been running along and parallel to the diabase body.  Is it a dike or a sill - or both?

16.8 – Walk through a cut in a large, fallen tree.

16.9 – Turn slightly L to pass through an area of discarded items and cross an old roadbed.

17.1 – Cross a small creek.

23-D: Note the active floodplain of the creek here, and at a slightly higher level, a terrace that represents a former floodplain.

17.2 – Cross another small creek.

17.3 – Cross a wide roadbed and start to walk through a more open forest.

23-E: Here to the right is an old canal, or possibly an abandoned river channel, parallel to the Eno.

17.4 – A narrow cut passage takes you through a large, fallen tree.

17.6 – Start a small ascent to reach higher ground and soon begin to parallel a wide roadbed, L. To the R is the Eno River far below you.

23-F:   Here is a huge bluff with exposure of coarse pebbly sandstone.

17.9 – The trail turns slightly L, then R to follow the roadbed.

23-G:  Here we are walking along an even more impressive cliff, this one on the inside of a bend in the river - a cut bank.  This is the point where Little River and Eno River merge (Figure 23-G).

18.0 – Go slightly R as the trail leaves the roadbed.

18.1 – Turn L, then R, onto another wide roadbed. Soon stay straight, by a junction, to go through an open area.

18.2 – Traverse a narrow, old, roadbed as the trail passes a swampy area, R.

18.3 – Turn R to leave the roadbed, onto a narrow footpath.

23-H:  Begin to encounter diabase again, apparently another sill.  The typical colors and shapes of diabase chunks should be familiar by this time (Figure 23-H).

18.4 – Cross a water run (may be dry).

18.5 – Cross another roadbed.

23-I:    More diabase.  We are walking in and out of the sill.

23-J:   The large dark rocks to the right may look like diabase from a distance, but look closer.  They are actually coarse pebbly sandstone, probably from the baked contact zone adjacent to the diabase sill.

18.7 – On stepping stones cross a water run. Soon begin a short ascent.
More diabase here; see if you can roughly locate the top and bottom of the diabase sill.

23-K:  Along this stretch be on the lookout for small pieces of fossil ("petrified") wood.

23-L:   Huge chunks of red and white micaceous sandstone, again possibly affected by the diabase intrusion.

19.0 – The trail turns R, onto a wide path. Soon pass, R, a small clearing with views of the Eno River below.

19.1 – The path curves to the L, but you need to stay R to remain on the trail.

23-M: Here is perhaps the most impressive bluff above the river.  Many streams and rivers in the Piedmont and Coastal Plain have steep bluffs only on their south side, as here.  The north side is very flat.  This stream valley asymmetry may be ascribed to more intense chemical weathering, and therefore soil formation, on the north, which receives more sunlight.  In addition, the harder diabase may be more prevalent on the south.  From here to the end of this trail section, below the trail, there are excellent exposures of sedimentary rocks on the faces of some of these bluffs and along the river’s edge.  They include cross-bedded sandstone and conglomerate (Figures 23-M1, M2, and M3).

23-N:  More diabase.

23-O:  Here the diabase is lumpy looking. This is a result of a coarser grain size than earlier.  Typically, the edges of a dike or sill will have a fine grain size due to rapid cooling in contact with the “country rock”, but in the center of a thick dike or sill, the magma cools more slowly and the crystals grow larger.

23-P:  More diabase.

19.6 – After passing a boundary marker, R, cross some abandoned railroad tracks.

23-Q:  Here by the tracks you see some huge fresh blocks of diabase, probably blasted.  Note how some are splitting apart, the result of freeze-thaw cycles that works to widen cracks, as water enters the crack, freezes and expands, then thaws again.

19.7 – On a footbridge, cross over a large drainage pipe and turn R to parallel a creek.

23-R:  If you look at the eroded creek bank here, you can see material deposited by the creek and by down-slope movements.  Note that there are chunks of the two rock types we have been seeing - diabase and sandstone, in this alluvium.

23-S:  Here there is a nice outcrop of diabase in the creek, with well-developed jointing.

19.8 mi – Reach Old Oxford Highway. This is the western terminus of the Falls Lake Trail.
To continue on the Mountains-to-Sea Trail, turn R to walk along the narrow shoulder on a short bridge over the Eno River and then L to cross the road onto Snow Hill Road. A quick L reaches a parking area for Penny’s Bend.

End of Trail Section 23

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